1. Technical Field of the Invention
The present invention relates to an electrooptical unit having an electrooptical panel and a circuit board overlapped and disposed therein, and to an electronic apparatus which uses the electrooptical unit. More particularly, the invention relates to a structure of electrical connection to panel-side terminals formed on the electrooptical panel.
2. Description of the Related Art
Various electronic apparatus including mobile phones such as shown in FIG. 2, are comprised of a lower case 6, a circuit board 7 formed with various electrical circuits for this mobile phone 1 to function, an illuminating unit 10, a light diffusing sheet 8, a liquid crystal panel 400 as an electrooptical panel for carrying out various display, and an upper case 9, which are overlapped on top of each other in that order. The illuminating unit 10 is comprised of a light source 11 constituted of an LED or the like, a light guide plate 12, a first reflecting member 15, and a sheet-like second reflecting member 17.
In the illuminating unit 10, the light guide plate 12 is formed with an active area 121 as a rectangular concave portion for disposing the liquid crystal panel 400 therein. In the active area 121, in the corner at the front end of a bottom wall 124, a rectangular through hole 125 for electrically connecting the liquid crystal panel 400 with the circuit board 7 is formed. In the first reflecting member 15, three side wall portions 151, 152, 153 enclosing the periphery of the rectangular active area 121 of the light guide plate 12 on three sides and a bottom wall portion 154, which is overlapped under the bottom face of the active area 121, are formed. A rectangular through hole 155 is also formed in the bottom wall portion 154 at a position where the through hole 125 of the light guide plate 12 overlaps therewith.
Accordingly, as shown in FIG. 15, at the upper side of the circuit board 7, when an electrooptical unit 100 is constituted of the first reflecting member 15, the light guide plate 12, the light diffusing sheet 8, and the liquid crystal panel 400 being overlapped on top of each other, although the first reflecting member 15 and the light guide plate 12 are interposed between the circuit board 7 and the liquid crystal panel 400, the circuit board 7 and the liquid crystal panel 400 face each other via the through holes 125 and 155. Accordingly, when a rubber connector 60 is made to be sandwiched and held between the circuit board 7 and the liquid crystal panel 400, the connector electrodes of the rubber connector 60 come into contact with and are pressed to I/O terminals 481 of the liquid crystal panel 400 by the elasticity, and come into contact with and are pressed to I/O terminals 781 of the circuit board 7 by the elasticity. Accordingly, it is possible to electrically connect the I/O terminals 481 and 781 together between the liquid crystal panel 400 and the circuit board 7.
In the electrooptical unit 100 structure as described above, in the liquid crystal panel 400, as shown in FIG. 16, liquid crystal (not shown) is held between a first transparent substrate 410 and a second transparent substrate 420 adhered together with a predetermined gap being interposed therebetween. Further, on the sides of the first transparent substrate 410 and the second transparent substrate 420 facing each other, electrode patterns (not shown) are formed of ITO film (Indium Tin Oxide; a transparent conductive film).
Herein, in an area 425 of the second transparent substrate 420 extending past the first transparent substrate 410, by means of an anisotropic conductive film which is formed using the forming process of the electrode patterns, terminals (not shown) for COG-mounting a driver IC 490 by means of an anisotropic conductive material, the I/O terminals 481 for inputting and outputting signals to the driver IC 490, and terminals (not shown) for mounting voltage-boosting capacitors 91, which are mounted outside the driver IC 490 by means of an anisotropic conductive material, are formed. The I/O terminals 481 are, as described while referring to FIG. 15, electrically connected with the I/O terminals 781 of the circuit board 7 via the rubber connector 60.
However, in a conventional electrooptical unit 100, the terminals formed in the liquid crystal panel 400 are made of an ITO film, which is formed at the same time as the electrode patterns for driving pixels, and since such an ITO film has a large contact resistance and a large unevenness in film thickness, when electronic components are electrically connected with the liquid crystal panel 400, the following disadvantages may often occur.
First of all, as the terminals having the surface mount type capacitors 91 mounted thereon are formed of ITO film, such disadvantages as a large contact resistance, and varying circuit constants may often occur.
Further, as the I/O terminals 781 of the circuit board 7 are gold plated on the surface thereof, at the points where they come into contact with the connector electrodes of the rubber connector 60, the contact resistance is small while the rubber connector 60 is compressedly connected therebetween and resistance variation over time hardly occurs; whereas, as the I/O terminals 481 of the liquid crystal panel 400 are formed of ITO film, at the points where the I/O terminals 481 of the liquid crystal panel 400 come into contact with the connector electrodes of a rubber connector 60, disadvantages occur such as the contact resistance being large only while being compressedly connected therebetween and the resistance increasing as time passes. Such contact resistance problems, when display is carried out by means of the liquid crystal panel 400, cause problems such as the panel not illuminating or illuminating dimly.
Furthermore, in the electrooptical unit 100, it is necessary to extend many electrode patterns from the driver IC 490 to an image display area 401 of the liquid crystal panel 400. Furthermore, as the periphery of the mounting area of the driver IC 490 contributes substantially little to the display, there is a demand, to reduce these areas formed with terminals by reducing the pitch of the I/O terminals 481.
However, as the rubber connector 60, which electrically connects the I/O terminals 481 of the liquid crystal panel 400 with the I/O terminals 781 of the circuit board 7, is structured such that the connector electrodes elastically come into contact with the terminals, it is necessary to provide a considerably large pitch for the connector electrodes. Therefore, conventionally, since it is necessary to also provide a large pitch for the I/O terminals 481 in accordance with the pitch of the connector electrodes of the rubber connector 60, in the liquid crystal panel 400, it is impossible to make the area for forming the I/O terminals 481 smaller. Therefore, in the liquid crystal panel 400, a problem occurs in that it is necessary to provide a large area which does not contribute to the display of images. Furthermore, as the wiring length of the electrode patterns is large, another problem occurs in that the resistance thereof becomes large, and the voltage of the input signal is decreased.
In view of these disadvantages as described above, an object of the present invention is to provide an electrooptical unit which enables electronic components to be electrically connected satisfactorily to the electrooptical panel, and an electronic apparatus using this electrooptical unit.
Furthermore, another object of the present invention is, even when the I/O terminals of the electrooptical panel is formed with a small pitch, to provide an electrooptical unit which enables electrical connection to be established with the circuit board via a rubber connector or the like, and an electronic apparatus using this electrooptical unit.